The present invention generally relates to ram air turbines of the type used on aircraft to drive backup electric or hydraulic power systems and, more particularly, to a ram air turbine having an in-line speed increasing planetary gearbox for driving an electrical generator or hydraulic pump.
Ram air turbine power systems (RATS) are generally known in the aerospace industry for use in driving auxiliary power systems in the event of a primary system failure. Commercial aircraft manufacturers install RATs as an emergency form of power when the main engine generators or hydraulic pumps are not operating. The ram air turbine power system is commonly stored within the wing or fuselage of an aircraft for deployment into the air stream when needed. When called upon for electrical power, the RAT is deployed into the air stream, typically by swinging it out from its wing or fuselage compartment at the end of a support strut, and functions similar to a windmill by extracting energy from the flowing air along the aircraft in flight. The ram air turbine portion of the RAT typically includes two or more turbine blades adapted to be driven by the air stream, to provide a rotary output which can be used to drive an electrical generator, a hydraulic pump or both. Such ram air turbines are commonly equipped with a speed control governor for altering turbine blade pitch angle, or feathering, to achieve a substantially constant turbine rotational speed despite variations in air speed or load.
When designing aircraft components, important factors to address are size, weight, and reliability. In an effort to reduce the physical size, also referred to as xe2x80x9cenvelopexe2x80x9d, of an electrical generator or other power source device that is driven by a RAT, one method is to increase the speed at which the generator or other power source device operates. But the RAT turbine may have an optimum speed that is slower than the increased generator speed. Prior art, for example, U.S. Pat. No. 5,484,120, teaches the use of a gear train as a means of transmitting shaft rotation up through a hollow support strut between the RAT turbine and a driven device at the top of the support strut within the aircraft, using spur gears and bevel gears. The use of such a drive shaft extending through the support strut to drive a power source device within the aircraft is comparatively long and heavy relative to using a short drive shaft to drive the power source device adjacent to the RAT turbine, and the spur gears and bevel gears may sustain a relatively high gear tooth loading, detracting from reliability. The problem of reducing generator envelope and weight is not addressed.
As can be seen, there is a need to reduce the envelope and weight of RATs while improving their reliability. There is also a need for reducing the envelope and weight of the generator or other power source device driven by the RAT turbine. Moreover, there is a need for providing an efficient arrangement of components in the RAT.
The present invention reduces the envelope and weight of RATs while improving reliability by using a gear train with reduced tooth loads. The present invention also reduces the envelope and weight of the generator or other power source device driven by the RAT turbine by increasing the speed of the power source device. Moreover, the present invention provides an efficient in-line arrangement of components in the RAT by keeping the turbine, the driven power source device, and gearbox components coaxial to improve overall packaging of the RAT power system.
In one aspect of the present invention, a ram air turbine power system includes a ram air turbine having a turbine shaft projecting rearward, and turbine blades for rotating the turbine shaft; a power source device having a rotatable power shaft for generating power in response to rotation of the power shaft for providing a power source. The power shaft has a generally hollow tubular shape defining a rear end, and the turbine shaft extends coaxially within the power shaft and also has a rear end. The ram air turbine power system also includes a gearbox housing a gear train, where one end of the gear train is connected to the power shaft near the rear end of the power shaft and the other end of the gear train is connected to the turbine shaft near the rear end of the turbine shaft so that the rotating turbine shaft drives the power shaft through the gear train.
In another aspect of the present invention, a gearbox is adapted for inline driving of a power shaft by a turbine shaft in a ram air turbine power system having a ram air turbine with turbine blades for rotating the turbine shaft and having a power source device where the power shaft defines front and rear ends and is supported to rotate within the power source device for driving a power generation apparatus to provide a power source. The gearbox includes a gear train having a driven gear and a driving gear. The driven gear is connected to the power shaft near the rear end of the power shaft and the driving gear is connected to the turbine shaft near the rear end of the turbine shaft whereby the rotating turbine shaft drives the driving gear, the driving gear rotates to drive the driven gear through the gear train, and the driven gear drives the power shaft.
In yet another aspect of the present invention, a ram air turbine power system includes a ram air turbine having a turbine shaft projecting rearward, and turbine blades for rotating the turbine shaft. The ram air turbine power system also includes an electrical generator for providing an electrical power source. The electrical generator has a rotatable power shaft. The power shaft has a generally hollow tubular shape defining a rear end, and the turbine shaft extends generally coaxially within the power shaft and also has a rear end. The ram air turbine power system also includes a gearbox housing an epicyclic star gear system. The epicyclic star gear system has an output gear and an input gear, the output gear may be a planetary sun gear, which is spline coupled to the power shaft near the rear end of the power shaft, and the input gear may be a planetary ring gear, which is spline coupled to the turbine shaft near the rear end of the turbine shaft, whereby the rotating turbine shaft drives the input gear, the rotating input gear drives the output gear through a gear train, which may include planet gears supported on a stationary bearing housing, and the output gear drives the power shaft, whereby the power shaft rotates at a greater speed than the turbine shaft.
In still another aspect of the present invention, a method for power generation includes the steps of, first, deploying a ram air turbine having a turbine shaft projecting rearward, and turbine blades for rotating the turbine shaft; second, using the ram air turbine to drive an electrical generator for providing an electrical power source, the electrical generator being driven by a rotatable power shaft, the power shaft having a generally hollow tubular shape defining a rear end, the turbine shaft extending generally coaxially within the power shaft and also having a rear end; and, third, driving the rotatable power shaft of the electrical generator through a gearbox including an epicyclic star gear system, the epicyclic star gear system having an output gear and an input gear. The output gear may be a planetary sun gear, spline coupled to the power shaft near the rear end of the power shaft, and the input gear may be a planetary ring gear, spline coupled to the turbine shaft near the rear end of the turbine shaft, whereby the rotating turbine shaft drives the input gear, the rotating input gear drives the output gear through a gear train, which may include planet gears, and the output gear drives the power shaft, whereby the power shaft rotates at a greater speed than the turbine shaft.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.